I would suggest you try growing in a completely different area of your garden rather than in the plot which has the problem. Others more know than me of these two moths may say differently.

I know nothing about this moth, but I do about something similar called alium leaf miner.
I'm not convinced growing on a different plot will help unless you cover the area with netting to keep it out. All it means is that the moth will find your plants from wherever they are hiding and do their nasties. Also, check out the life cycle of the moth to find out best planting times, etc, etc,

I may be wrong but; I think you are getting you leek/onion problems mixed up!

e.g. Leek moth and Onion White rot!

Leek moth problems are annual and only occur if the moth is around,so some years this won't necessarily be the case!

Unlike onion white rot which is in the soil and then yes! you are well advised not to plant any 'alliums' in that are for at least ten years!

As regards a cure for 'moths' I drench the soil at planting with Armillatox, which is a Jeyes fluid smelling detergent that disguises the allium odour!

I do this for all flying insects such as root flies and yes....the cabbage white!

Whether it is the right thing to do or not, I don't know, but I have to say it has worked for me for years!

There is no cure for Onion White rot at least to the amateur. But if you can get hold of some 'Tilt' then you stand a chance!

Forgot to add this link to an article on leek moths;

http://www.thegardenersalmanac.co.uk/Data/Leek%20moth/Leek%20moth.htm

Don't think Tilt is made anymore. I've got quite a large bottle though:)

Regarding armillatox though, they reckon doing this for white rot

Drench the ground at the dilution rate 1:100 using 5 litres per square metre.
Apply prior to and after digging.
Plant after 3 weeks.